The invention relates to an antenna device for reading electronic labels and a system for reading electronic labels.
The field of the invention is that of radio frequency identification or RFID applied in particular to the reading of electronic labels (tags) apposed to objects grouped together in a small area.
An electronic label comprises a chip and an antenna, both buried in any support, generally of small size. The electronic label functions according to a contactless mode by means of an input-output interface consisting of the antenna. The antenna is of small size in relation to the dimensions of the electronic label.
The electronic label is read (or written to) by a reader which has a reading antenna for effecting an electromagnetic coupling with the electronic label.
So that the electromagnetic coupling is sufficient despite the small dimensions of the electronic label antenna, one solution consists of the reader being close to the electronic label.
These conditions are not always achievable in practice.
Another solution described in patent application WO 97/49076 consists, as shown schematically in FIG. 1, of using, between the antenna 10 of the reader 1 and the antenna 20 of the electronic label 2, an auxiliary passive antenna 30, sometimes referred to colloquially as a parasitic antenna, which begins to resonate at a given frequency under the action of a radio-frequency signal. When it is thus tuned to the given frequency, this auxiliary passive antenna 30 reinforces the electromagnetic coupling M1 between the reader 1 and the electronic label 2, by focusing the electromagnetic illumination of the antenna 10 of the reader 1 onto the antenna 20 of the electronic label 2. This reinforcement is obtained by electromagnetic coupling M2 between the antenna 10 of the reader and the auxiliary passive antenna 30 and by electromagnetic coupling M3 between the passive antenna 30 and the antenna 20 of the electronic label.
When it is wished to read numerous electronic labels grouped together in the same reading zone of the reader, it is possible to multiply the passive antennae as described above, but the passive antennae, then close to one another, will mutually interfere with each other.
It is also possible to use devices comprising as many active antennae as there are electronic labels. However, this multiplication of the active antennae is expensive since it results in a multiplication of the commands managing the transmission and reception radio frequencies of these active antennae.